Syrian opposition and rebel leaders meeting in Istanbul ahead of U.N.-convened talks set to start in Geneva next week have reaffirmed their longstanding demand for the departure of President Bashar al-Assad and his ruling coterie, saying there could be no political solution to the civil war while he remains in power.

Arguing that recent battlefield gains by the insurgents are shaping “a new political reality” in Syria, rebel leaders argue that only the backing of Iran and Russia is prolonging the conflict. “The current coordination between the rebel factions can contribute to the acceleration of the liberation process of Syria from the Assad regime,” says Khaled Khoja, the president of the Western-backed Syrian National Coalition (SNC)

In a press statement, Khoja maintained that the seizing by rebel factions over the weekend of Jisr al-Shughur, a key town in northern Syria, marks “a turning point” in the conflict that has left more than 200,000 people dead.

On Friday, the United Nations envoy for Syria, Staffan de Mistura, briefed the Security Council on the prospects for talks in Geneva among some of the combatants. Diplomats, however, say the chances of any breakthrough next week in Switzerland are remote.

With jihadists from the so-called Islamic State and al-Qaida affiliate Jabhat al-Nusra excluded, and rebels scoring recent major military gains, the opposition has little reason for negotiating. And with President al-Assad’s leverage reduced because of government setbacks, the regime has little interest in engaging in serious talks. In the past, the Assad regime has only engaged in talks when officials in Damascus have felt they were in the driving seat.

On Friday, de Mistura himself played down the possibility of any movement being made next week toward a peace deal, and he cautioned the Security Council there was no real willingness on behalf of the participants to consider a political solution. He warned the negotiations should be seen as “talks about talks.”

“This is not a Geneva III,” he later told reporters in New York, referring to previous peace negotiations on Syria that failed because of disagreements on whether President Assad must quit office ahead of a political transition.

In the past month, moderate rebels in league with Jabhat al-Nusra have scored a series of victories on the battlefield, capped by their capture on Saturday of Jisr al-Shughour in northern Syria following three days of a rebel assault.

Insurgents have battled off and on to secure the highly strategic town since government forces seized it in June 2011 in the early days of the conflict. Jisr al-Shughour's fall now exposes two nearby regime bases that can only be supplied by air, and the government’s reaction with airstrikes on Jisr al-Shughour since its capture is testimony to the seriousness of the loss for the Assad regime.

In the seesawing war, the last few weeks have seen the regime suffer a series of reversals that have some analysts arguing the Assad government is weaker now than at any other point in the conflict.

“Despite constant Western media assessments that Assad’s situation is secure, the reality is that the Syrian war is one of attrition,” according to former U.S. Ambassador to Damascus Robert Ford, who is now a senior fellow at the Washington-based Middle East Institute. “And minority regimes usually do not fare well in prolonged wars of attrition,” he said in a paper for the research organization.

“Bashar al-Assad’s regime in Syria did not have a good winter,” the former ambassador continued. “His forces lost a provincial capital, Idlib, and despite repeated efforts could not even seize northern and eastern suburbs adjoining Damascus. There were also failures in Aleppo and Dara‘a. He had to relieve heads of two of the regime's four secret police services. The economic situation worsened.”

Although Ford says he sees signs that Assad’s recent setbacks may spell the end of his regime, he cautions the embattled president still enjoys “some military advantages and support from Iran and Russia,” which likely will help to prolong the conflict.

Analysts say another advantage Assad has been able to rely on in the past is rebel infighting, especially between moderates and jihadists. With moderate rebel militias collapsing and joining more hardline Islamist brigades, divisions, at least temporarily, have been papered over. Islamist brigades have been cooperating with Jabhat al-Nusra - as they did in engineering the fall of Jisr al-Shughour and the capture a few weeks ago of Idlib, only the second provincial capital to be lost by the regime.

In the streets of Jisr al-Shughour, the black flags of al-Nusra could be seen flying in videos posted of the town after its fall.

Earlier this year, Assad’s forces were menacing the rebels in districts they hold in the northern Syrian town of Aleppo and threatening an encirclement that would have severed insurgent supply lines to Turkey. With the encirclement just a handful of kilometers from being completed, Assad boasted that 2015 would see his victory over the rebels in a civil war.

Rebel commanders and analysts say Assad’s forces were overstretched in Idlib. Noticeably absent in the defense of the city in the country’s northwest were Iranian coordinated foreign Shi'ite militiamen and Lebanese Hezbollah fighters, whom the Syrian government has relied on for past gains as well as to organize local fighters from Assad’s minority Alawi sect, an offshoot of Shia Islam.

Many Shia militiamen from Iraq who had been fighting alongside the Syrian army started to return last year to neighboring Iraq to assist in the fight back against the Sunni militants of Islamic State, also known as ISIL or ISIS, who have seized a swath of western and northern Iraq.